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Research |
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Tufts Micro & Nano Fabrication Facility (TMNF) |
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Tufts University |
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Please send examples of research projects being conducted in the lab to Prof. White for inclusion in this page. |
Micromachined Shear Stress Sensors for in-situ Monitoring of Surface Forces in ChemiMechanical PlanarizationA PDMS microstructure is being developed to measured the interaction forces that occur between a wafer and a polishing pad during CMP. The PDMS structures deflect in response to fluid forces and solid-solid contact forces. An optical method is used to monitor structure deflection in-situ.
Student: Minchul Shin, ME PhD student, Doug Gauthier and Andrew Mueller, ME Masters of Science students. Advisor: Prof. White, ME |
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Left: SEM image 30 micron diameter, 100 micron tall PDMS post-in-well developed for the CMP shear stress sensor project. Right: angled light microscope picture showing a portion of the array with different sized PDMS posts-in-wells. |
Micromachined Pressure Sensor Arrays for Aeroacoustics
Design, fabrication, and characterization of a surface micromachined, front-vented, 64 channel (8X8), capacitively sensed pressure sensor array is underway. The array was fabricated using the MEMSCAP PolyMUMPs process, a three layer polysilicon surface micromachining process with additional postprocessing fabrication steps (release, packaging, Parylene coating) carried out at Tufts. The computational results for the design, including mechanical components, environmental loading, fluid damping, and other acoustic elements predicts single element sensitivity of 0.65 mV/Pa at the gain stage output in the 400-40,000 Hz band. A laser Doppler velocimetry (LDV) system
Student: Joshua Krause, ME PhD student. Advisor: Prof. White, ME |
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Light microscope image of the array (left) and SEM image of a single element (right). The elements are made of 3.5 micron thick polysilicon with a 2 micron air gap to the bottom electrode. The wires (and writing) are Cr/Au on polysilicon. Element diameter is 0.6 mm and pitch is 1.3 mm. |
Calibration Targets for Dual Emission Laser Induced Fluorescence (DELIF)Calibration wafers have been fabricated to calibrate an optical measurement technique called Dual Emission Laser Induced Fluorescence (DELIF), which is used to determine fluid film thickness between a glass wafer and a polishing pad during Chemical Mechanical Polishing (CMP). Sqaure wells measuring 1mm2 and 0.25mm2 are etched into these glass wafers to known depths (up to 130um). The necessary well etch depth depends on the surface roughness of the polishing pad. In order for fluid layer thickness difference under the wells to be detectable, the well depth should be at least 3 times the surface roughness of the pad.
Student: Caprice Gray, ME PhD student. Advisors: Prof. Rogers, Prof. Manno, Prof. White, ME |
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(Left) Photograph of etched glass calibration wafers used to determine thin fluid film thickness during DELIF. (Right) A light microscope picture of a single 1mm2 calibration well 23 microns deep. |
Micromolding of Aqueous-Derived Silk StructuresThere is enormous potential for biopolymers in MEMS applications. In MEMS devices biopolymers could function as membranes or optical components. Devices which demand outstanding biocompatibility, such as implantable sensors, could be packed in or fully manufactured from biopolymers materials. The challenge today exists in understanding critical processing parameters in manufacturing structures with micron and submicron level features from biopolymers. In this research, the development of a micromolding technology, to produce microstructures from aqueous derived silk solutions is studied. In particular, well-defined cellular and tissue culture substrate (scaffold) fabrication is used as a model to study manufacturing methods. The manufacturing challenges consist in counteracting shrinkage caused by solvent evaporation, producing well defined porous structures and demolding of delicate structures.
Student: Konstantinos Tsioris, ME MS student. Advisor: Prof Wong, ME |
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(Left) SEM image of silk fiber (crossection 100 x 100 μm) as part of well defined scaffold layer. (Right) PDMS microchannel system (individual channels: width 100 μm x height 250 μm) produced with SU-8 photolithography. |
Thermal Design and Fabrication of Microscale HeatersMicroscale heaters with integrated thermistors were fabricated as an undergraduate research project. The devices use thin sputtered nickel films for both heating and sensing elements. The processes involved were standard photolithography, sputtering, and liftoff. Some of the heaters were functional, and some failed. Residual stresses, particles, and/or human error in processing appear to have caused the observed defect in some of the heater lines.
Student: Michael Rizzolo, ME undergraduate. Advisor: Prof Wong, ME |
Lab-on-a-chip Devices for Dynamic Seeding of Bone CellsLab-on-a-chip devices have become increasingly popular as quick and easy diagnostic and experimental tools due to their size, flexibility in application, and relative ease of manufacturing and use. The development of customizable lab-on-a-chip features, such as surface patterning or coatings, can have widespread application. This research established low-cost and simple calcium phosphate coating capabilities on a silicon wafer using electrophoretic deposition, as well as the ability to pattern such a coated wafer with photoresist. The coated and patterned wafer was used to evaluate the ability of bone cells to adhere to a microchannel surface under flow, or dynamic seeding conditions.
Student: Erica Belmont, ME MS student. Advisor: Prof Matson, ME |
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(Top Left) Silicon wafers, diced to 36mmx36mm, coated with calcium phosphate and one uncoated wafer chip for comparison (Bottom Left) Calcium phosphate coated wafers with microchannels patterned in 100um thick SU-8 photoresist (Right) SEM image showing cross-section of calcium phosphate coating, approximately 15um thick, on silicon wafer . |
Hair-like Surface Shear Force SensorsMEMS shear sensor and shear sensor arrays for surface shear force measurement are under development. The shear sensor consists of 50-250 mm high SU-8 posts resting on a flexible base. A capacitive sensing scheme is used for detecting the vector force applied to this post. Four different size hair-sensors and hair-sensor arrays are designed. The sensitivity and dynamic range of each design are computed. Predicted dynamic range is on the order of 60 dB. The most sensitive design is expected to measure forces on the order of 1 mN in a 500 Hz band. The least sensitive design is expected to be able to measure forces as large as 10 mN. A fabrication process for producing the sensors is described and fully demonstrated. Characterization of the sensor sensitivity, frequency response, resolution, and dynamic range is ongoing.
Student: Shuangqin Liu, ME PhD student. Advisor: Prof White, ME |
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Microscope picture of the hair sensor arrays. These are 50 micron high posts with all the associated capacitive readouts. |
Copper Nanowires for Crossed-Nanowire TransistorsCopper nanowires (with a thin copper oxide sheath) were grown on a silver substrate for use as the gate in experimental crossed-nanowire transistors. The nanowires are grown by the electroplating of copper through anodized aluminum templates, which were later etched. The nanowires are ~150nm in diameter and 5um in length. Other potential applications include anodes in super-capacitors, frictional elements, and high surface area electrodes for sensing.Student: Sam MacNaughton, ECE MS student. Advisor: Prof Sonkusale, ECE |
Development of a Microfabricated Perfusion System for Vascularized Tissues
There is a critical clinical demand for tissue-engineered, three-dimensional constructs for tissue repair and organ replacements. Upon initial implantation, three-dimensional (3-D), tissue-engineered (TE) constructs maintain functionality and interface with the human body. In the long-term, however, necrosis occurs at the core of the construct because of limited oxygen and nutrient diffusion into the deeper layers of the TE construct. The diffusion limit of oxygen and nutrients into 3-D TE constructs is a major obstacle in the tissue engineering field. The clinical success of future 3-D TE constructs depends on developing the capability to deliver nutrients to larger engineered tissue systems.
Student: Lindsay Wray, BME PhD student. Advisor: Prof Kaplan, BME |